It has been known that epoxy resin compositions using acid anhydride based curing agents provide transparent cured materials and are suitable as sealing media of optical semiconductor devices such as light emitting diodes, photodiodes and the like.
However, as optical semiconductors have become more sophisticated in recent years, higher performance has been required as performance of sealing media of the semiconductors, and cured materials have been demanded which are excellent in heat resistance, moisture resistance, light resistance and weather resistance, low stress, and further excellent in thermal shock property and adhesion. Therefore, sufficient properties have become hard to obtain in compositions having as the main ingredient epoxy resins of organic resin structure such as bisphenol A epoxy resin, bisphenol F epoxy resin, (3′,4′-epoxycyclohexyl)methyl-3,4-epoxycyclohexane carboxylate and the like that have conventionally been used.